Information presenting apparatuses are known which compute information (that includes a state estimator and called a “track”) of a target based on observed values supplied by sensors, and display a result of the computation.
FIG. 11 is a block diagram showing an example of the known information presenting apparatuses, which includes a track maintenance unit 101, a track generation unit 102, and an operation and display unit 103.
The track maintenance unit 101 computes a correlation between each observed value supplied from sensors and a “confirmed track” (that may be simply called the “track” below) of a target, and updates the track using each observed value which has the relevant correlation. In addition, the track maintenance unit 101 outputs each observed value which has no correlation with the track of the target to the track generation unit 102. The track maintenance unit 101 also outputs the track of the target, which has been updated using each observed value which has the relevant correlation, to the operation and display unit 103.
The track generation unit 102 handles each observed value input from the track maintenance unit 101 (i.e., observed value which has no correlation with the track of the target), as a tentative track which has the potential of a track of a target. More specifically, the track generation unit 102 computes a correlation between the input observed value and an existing tentative track. If there is no correlation, the track generation unit 102 handles the relevant observed value as a new tentative track. If there is a required correlation, the track generation unit 102 updates the existing tentative track using the relevant observed value.
In addition, the track generation unit 102 computes a likelihood ratio for each tentative track by means of an SPRT (Sequential Probability Ratio Test) method. Based on the computed likelihood ratio, an upper limit threshold TU, and a lower limit threshold TL, the track generation unit 102 determines whether the relevant tentative track is determined to be a confirmed track of the corresponding target or is abandoned. The upper limit threshold TU is a value used when the tentative track is determined to be a track of the target. The lower limit threshold TL is a value used when the tentative track is determined to be a track by a false alarm. Here, the false alarm occurs where a non-target event exceeds a target-detection criterion and is identified as a target.
The display unit 103 displays the track of each target, which is input from the track maintenance unit 101, on a display screen.
FIG. 12 is a flowchart showing a specific example of the operation flow that is applied to each tentative track and is executed by the track generation unit 102 in the conventional information presenting apparatus.
As shown in the flowchart, the track generation unit 102 receives each observed value from the track maintenance unit 101 (see step S101). The track generation unit 102 then computes a correlation between the received observed value and each tentative track (see step S102) so as to determine a correspondence relationship between the observed value and the tentative track.
The track generation unit 102 executes an operation from step S103 to step S108 based on (i) a first error rate (called “Type I error”) of an error such that a track by a false alarm is determined to be a track of a target, (ii) a second error rate (called “Type II error”) of an error such that a track of the target is determined to be a track by a false alarm, (iii) a probability of detecting a target, (iv) a probability of detecting a false alarm, (v) the number of scans of a tentative track, and (vi) the number of updates of the tentative track for the scanning thereof.
The track generation unit 102 computes a likelihood ratio for each tentative track (see step S103). The track generation unit 102 then repeats an operation from step S104 to step S108 for each tentative track.
The track generation unit 102 determines whether or not the likelihood ratio computed in the above step S103 is less than or equal to a lower limit threshold TL (see step S104). If the likelihood ratio of the relevant tentative track is less than or equal to the lower limit threshold TL, (i.e., “YES” in step S104), the track generation unit 102 abandons the tentative track (see step S108) and executes a process applied to the next tentative track. If the likelihood ratio of the relevant tentative track is greater than the lower limit threshold TL (i.e., “NO” in step S104), the track generation unit 102 determines whether or not the likelihood ratio computed in the above step S103 is greater than or equal to an upper limit threshold TU (see step S105).
If the likelihood ratio of the relevant tentative track is greater than or equal to the upper limit threshold TU (i.e., “YES” in step S105), the track generation unit 102 determines the tentative track to be a confirmed track (see step S106). The track generation unit 102 then outputs the relevant tentative track as a confirmed track to the track maintenance unit 101 (see step S107) and executes the process applied to the next tentative track. If the likelihood ratio of the relevant tentative track is less than the upper limit threshold TU (i.e., “NO” in step S105), the track generation unit 102 keeps the tentative track as itself (i.e., as a tentative track) and executes the process applied to the next tentative track.
For example, the track generation unit 102 performs the above-described operation for each scan of the tentative track.
FIG. 13 is a diagram that shows an example of the track displayed on a display screen 300 of the conventional information presenting apparatus. As shown in FIG. 13, the display unit 103 displays a track 201 (see a double circle) of a target on the display screen 300, where the track 201 has been determined (to be a track) by the track generation unit 102 and maintained by the track maintenance unit 101.
FIG. 14 is a diagram that shows an example of displaying, not only the track as shown in FIG. 13, but also all observed values supplied by the sensors as observed values 500 on the display screen 300.
In FIG. 13 or 14, the square indicated by the reference numeral 200 is shown for convenience to indicate the position at which an observed value for the target has been obtained, in comparison with the position of the track 201 of the target. Therefore, actually, no mark that indicates the position 200 is displayed on the display screen 300.